Equilux or Equinox: When exactly will Spring start?

People usually define the arrival of Spring as point of daylight hours increasing and the weather improving.

This generally occurs in the UK towards the beginning of middle of March, but with the Met Office dating the first day of Spring as March 1, the Spring Equilux happening today and the Spring Equinox happening next week, what exactly determines the start of Spring and can it be precisely dated?

Spring weather usually sees brighter and drier days

Spring Equilux

Today marks the Spring Equilux, a day which sees a change in the amount of daytime hours we see, as there are equal amounts of day and night-time hours. Sunrise occured at 06.41am and will set tonight at 18.41pm, therefore producing an equal split in the amount of day and night-time hours.

Met Office Meteorologist Martin Bowles explains how this equal split of hours is because of the ‘position and angles of the sun’ which then ‘produces this equal time’.

However, the Met Office marks the first day of Spring as March 1 because as Mr Bowles explains, this is when there is usually ‘more daytime than night’, hence showing that as the year progresses into March, the daylight hours have usually begun to increase.

Can the timing of Spring be precisely determined?

The Spring Equilux is not to be confused with the Spring Equilox, which is the first official astronomical day of Spring.

Spring Equinox

This year, the Spring Equinox will occur six days after the Equilux, happening on March 20, and also being a measure of the amount of daylight hours in comparison with the night.

Morgan Hollis from the Royal Astronomical Society explains that although the Equilux is more of a meteorological measure of Spring than the Equinox, they are very similar in nature as they also measure the ‘point of equal day and night’. With ‘nox’ being the Latin terminology for night and ‘lux’ being the Latin reference for day, this shows the connection between both Equinox and Equilux and therefore the equal measure between daylight and nighttime hours.

Mr Hollis continues that this is relates to “where the Earth is in relation to the sun” as “the motion and change in the alignment of the Earth as we orbit the Sun causes the Earth to tilt”, hence changing the time of “what point of the Sun faces the Earth”.

However, as Mr Bowles explained that the Equilux occurs when the sun rises and sets at the exact same time, this is not quite the same in regards to the astronomical Equinox, as although it still reflects an equal amount of daylight and nighttime hours, it is not quite as exact as the meteorological Equilux.

Mr Hollis also explains that the Solstice, which occurs twice a year, once at Winter and once at Summer, also relates to the daylight and nighttime hours. He explains that the Winter Solstice marks “nights becoming the longest and the days being the shortest”, but the Equinox “is the transition point”, as it marks that the days will now become longer than the nights.

Can the start of Spring be precisely measured?

Although the Spring Equilux and the Spring Equinox are indicators of Springtime due to the increase in the amount of hours we receive, a sign which many people see as the change from Winter to Spring, the exact date or definition of the beginning of Spring cannot be precisely determined or defined.

Mr Hollis points out that although “some people will define the Equinox as a the point of Spring”, it of course “depends on people's definition of Spring”, hence being something which cannot be exactly determined.

Mr Bowles then echoes this as he also explains that “people define Spring differently” and although Spring not only usually notices an astronomical change in the amount of daylight hours due to the motion and position of the sun, he explains that in regards to meteorology, Spring is usually noticed by a change in the weather.

However, Mr Bowles also refers back to the recent Beast From the East and the extreme cold weather which this produced at the beginning of March, this usually being the time in which the weather improves and also another usual indicator of Spring, showing that this is not always the case.

Although the Equilux and Equinox are meteorological and astronomical indicators of the beginning of Spring, what we usually expect from Spring in relation to its weather is due to be disturbed again.

This weekend the Beast from the East is due to return to the UK and bring with it another cold blast, so in regards to the sunnier, drier and slightly warmer weather we hope to see at this time of year, unfortunately Spring has not quite yet begun.